Method of forming the banjo and frame of a rear axle housing



ay 1934. s. SPATTA METHOD OF FORMING THE BANJQ AND FRAME OF REAR AXLE HOUSING OriginaLFiled Feb. 7, 1930 5 Sheets-Sheet 1 G. SPATTA 1,953,215

METHOD OF FORMING THE BANJO AND FRAME OF A REAR AXLE HOUSING May 8, 1934.

Original Filed Feb. 7, 1930 5 Sheets-Sheet 2 G. SPATTA 1,958,215

' METHOD OF FORMING THE BANJO AND FRAME OF'A REAR AXLE HOUSING May 8, 1934.

5 Sheets-Sheet 5 Original Filed Feb. 7, 1930 G. SPATTA May 8, 1934.

METHOD OF FORMING THE BANJO AND FRAME OF A REAR AXLE HOUSING -5 Sheets-Sheet 4 Original Filed Feb. 7, 1930 17 wh /22 0;? 'eo gpe Z0027?! EL ww:

Q Q RQ May 8, 1934. SPATTA I 1,958,215

METHOD OF FORMING THE BAN-I0 AND FRAME OF A REAR AXLE HOUSING Original Filed Feb. '1. 1950 s Sheets-Sheet 5' 68 7 2 7 7 [@910 g j Ii g Patented May 8, 1934 UNITED STATES PATENT OFFICE METHOD OF FORMING THE BANJO AND FRAME OF A REAR AXLE HOUSING George Spatta, Buchanan, Mich., assignor to Clark Equipment Company, Buchanan, Mich., a corporation of Michigan Claims.

This invention relates to the method of forming the banjo and frame of a war axle housing.

In my copending application, Seli -.1 No. 416,- 537. filed December 26, 1929, (Case 13), I :15- 5 closed a method of forming rear axle housing for vehicles, that method including a number of steps progressively performed upon a tubular blank to fabricate it into the finished article. The present invention primarily relates to one of the steps in this process, and I have illustrated my invention by showing a machine designed to perform a specific operation in that method, although I am aware that the invention is applicable to other similar processes. The specific machinesdisclosed herein are covered more fully in my copending application Serial No. 426,545, filed February 7, 1930, of which the instant application is a division.

Briefly, the steps in the process disclosed in my first above mentioned copending application consist of slotting the tubular blank, shrinking the end section of that blank to a smaller diameter, changng the shape of the walls freed by the slots in the blanks from their original shape,

which is that of part of a cylinder with a horizontal axis, into a difierent shape, namely, to parts of a cylinder with a vertical axis or vertical axes, and then spreading and shaping the blank to form the banjo of the housing. The

present invention relates specifically to the spreading and forming operation.

The preliminary changing of the shape of the wall of the blank is disclosed in full in my copending application, Serial No. 425,426, filed February 3, 1930, (Case 17), that operation being performed solely for the purpose of expanding the slot area sufficiently to permit inserting the punches that are employed to form the banjo of the housing in accordance with the teachings of the present invention. In this preliminary operation, the arcuate wa l sections between the oppositely disposed slots in the blank are changed into wall sections of a transverse cylinder, with a consequent stretching of the metal at the edge of the wall sections at the end section of the blank, that is, at the points of application of the dies to the blank. This preliminary spreading of the walls is accomplished without affecting the metal at the critical section of the blank since the dies do not reach that metal and shoe their operation is only one of reshaping the arcuate walls which they engage.

Banjo housings of the type that the machine disclosed in the instant application is designed to manufacture have a centrally located cylindrical portion whose axis is disposed transversely of the axis of the housing. This central cylindrical portion is provided with flanges which project radially inward from its opposite edges, those flanges serving as plates to which the covers and drive shaft casing of the vehicle are attached.

The depth of the web section between these flanges is materially less than the diameter of the blank from which the housing is made, and the banjo forming operation therefore must fold the edges of the mid-section of the blank over and inwardly to form the flanges and must spread the .web sections outward and form them into arcuate shapes so that they will lie on the circumference of the cylindrical banjo of the completed housing.

In the performance of this operation, the folding of the metal at the edges of the wall sections between the slots causes a gathering of metal in the flange of the banjo, this gathering compensating for the stretching that has occurred in these sections during the step of preliminarily spreading these wall sections. The operation of spreading the webs of thebanjo stretches the metal in those webs at points adjacent to the junction of the tubular end sections-of the housing with the slotted central portions of it, that is, at the critical sections of the blank.

By proper design of the dies, taking into consideration the wall thickness of the blanks, I am able to regulate the gathering of metal in the flange to such an amount that the thickness of the flange in the finished article is the same I of the metal to flow upon being bent under the conditions prevailing, and without definitely upsetting the metal in the flange.

The spreading and shaping of the web of the banjo, which causes stretching of the metal at the critical sections of the blank, also reduces the overall length of the blank, in one instance this reduction amounting to two inches. The metal drawn from the tubular end sections of the blank and through the critical sections is made to provide metal for the web section of the banjo, which section is of substantially longer diameter than the diameter of the tubular blank from which the housing is made.

The machine employed to carry out this step of the process preferably comprises a hydraulic forging press consisting of a vertically disposed cylinder and ram and a horizontally disposed cylinder and ram. The die structure consists of a stationary die block and a movable die block, each of these blocks being provided with clamping members which engage the tubular end sections of the blank and hold those sections in alignment during the performance of the operation.

A pair of forming punches are mounted in the press between the stationary and movable die blocks, and the blank that is to be forged in the machine is placed over these punches when they are in their normal or collapsed position.

The horizontal ram is connected to the movable die, and is operated by its cylinder to move that die horizontally to bring it into engagement with the stationary die, the movement being limited by adjustment of the clamping member. The punches are also moved by this operation, and the work and punches are thereby brought into alignment with the vertically disposed ram. The vertical ram is then operated to engage the punches and expand them to thereby force the wall sections of the work into the dies to form those sections into the prescribed shape. The vertical ram is then withdrawn, this withdrawal closing the punches and contracting them away from the finished work, and the horizontal ram is then operated to withdraw the clamping engagement from the work to thereby permit its removal from the machine.

In the preferred embodiment of my invention, the rams of the machines are hydraulically operated, although I am aware other suitable modes of operation can be substituted within the teachings of my invention.

Now, to acquaint those skilled in the art with the teachings of my invention, reference is made to the accompanying drawings in which the preferred embodiment of it is shown by way of example, and in which:-

Figure l is an elevarional view of the forging press taken from the front or open side of it;

Figure 2 is an elevational side view of the press;

Figure 3 is a plan view of the punches and dies taken along the line 33 of Figure 1, looking in the direction of the arrows;

Figure 4 is a bottom side plan view of the wedge employed to operate the punches;

Figure 5 is a cross-sectional view taken along the line 5-5 of Figure 3 and showing the punch and die structure in its normal or open position;

Figure 6 is a view similar to Figure 5 showing the punch and die structure in its operated or closed position;

Figure 7 is a cross-sectional view of Figure 6 taken along the line 7-7 looking in the direction of the arrows;

Figure 8 is a cross sectional plan view of the punch and die structure taken along the line 8--8 of Figure 6, looking in the direction of the arrows;

Figure 9 is a cross-sectional view of the die taken along the line 9-9 of Figure 8, looking in the direction of the arrows;

Figure 10 is a view taken along the line 1010 of Figure 8 showing the details of the connection of the ram to the movable die;

Figure 11 is a fragmentary cross-sectional view taken along the line 1111 of Figure 6 showing the shape assumed by the sections of the blank adjacent the die at the completion of this step in the process;

Figure 12 is a cross-sectional view of the clamping members taken along the line l212 of Figure 8;

Figure 13 is a cross-sectional view of the operating wedge taken along the line 1313 of Figure 5 and showing the dovetail flange on that wedge;

Figure 14 is a perspective view of the blank at the completion of this step in the process; and

Figure 15 is a cross-sectional view taken along the line l515 of Figure 5 looking in the direction of the arrows and showing the details of the punches.

Referring to Figures 1 and 2 of the drawings now in more detail the forging press comprises a frame 1 which is of generally C-shape, and which has a flat table portion 2 adjacent its lower open end. The punch and die structure indicated generally at 3 is mounted on this flat table portion. A pressure flange 4 is formed integral with the frame and rises vertically above the upper surface of the table portion at the extreme outward end of that portion of the frame, this pressure flange serving as a stationary mount for the die structure and to resist the pressure placed on that die structure longitudinally of it.

A horizontal cylinder 5 is disposed adjacent the fiat table 2, and provided with a ram 6 which is adapted to operate over the upper surface of that table to control the operation of the die structure 3. Preferably, the cylinder 5 is provided with a cylinder head '7 which is held against the cylinder 5 by external bolts 8 which are threaded into the frame work 1 and provided with nuts 9 which bear against the outer surface of the cylinder head 7 to hold it on the cylinder 5.

This puts the walls of the cylinder 5 normally .under compression, as is well understood by those skilled in the art, and they are therefore better able to withstand the pressures built up within them in the operation of the machine.

A second cylinder 11 is disposed at the extreme end of the upper part of the frame work 1 with its axis perpendicular to the table surface 2, this cylinder 11 being provided with a ram 12 which is operated in a vertical direction to engage the punch and die structure to operate that structure in the manner which will be hereinafter more fully explained. Preferably the cylinder 11 is also provided with a cylinder head 13 which is held thereon by external bolts 14 and nuts 15 to place the walls of the cylinder 11 normally under compression so that they may better resist the pressures built up within them in the operation of the machine.

A control valve 16 is mounted on the frame work 1 of the machine in any convenient manner and arranged to be operated by the lever 17 to control the operation of rams 6 and 12. In the preferred embodiment of the machine shown in Figures 1 and 2, the cylinders 11 and 5 are hydraulically operated, although other suitable means for operating the rams of these cylinders may be substituted within the teachings of my invention.

The ram 12 is provided with a cross head 18 upon which the operating wedge is mounted, this cross head being provided with a projecting arm terminating in the boss 19 in which a guide rod 20 is fitted and held by a screw 21. The frame work 1 is provided with a collar 22 through which the guide rod 20 passes, the rod thereby preventing rotation of the ram 12 with respect to the frame work 1 during the operation of the ram, for

purposes which will be more fully brought out hereinafter. v 7

Preferably the frame work 1 is a metallic casting, and as such is provided with the usual reinforcing ribs and flanges the details of which form comprises an upper fiat surface 31 upon which The plates 47 and 48 are held on the forming the die structure is fitted and adapted to slide, this surface being provided with upwardly extending flanged edges 32 which serve as guides to prevent movementof the die transversely of the axis of the ram 6. The bed plate 30 is also provided with outwardly extending flanges 33 through which the bolts 34 are projected and threaded into the table top 2 to hold the bed plate thereon. The die/structure comprises a. stationary member 40 which consists of a forming die 41 located centrally of the member 40 and in alignment with the axis of the ram 6. Clamping members 42 and 43 are disposed on opposite sides of the forming member 41, the clamping members serving to grip the ends of the blank and to hold them in alignment during the performance of the forging operation by the machine.

The stationary die is held in the machine by the bolts 44 which are extended into the bed plate 30, and is held against movement longitudinally of the axis of the ram 6 by a spacing block 45 interposed between the back side surface of the die member 40 and the stop block 4 of the frame work.

The forming die 41 comprises a central formin; member 46 which has a forming surface 46 machined to the contour to which the web section of the banjo is to be formed. Batter plates 47 and 48 are disposed upon opposite sides of the forming block 46, these plates preferably being constructed of hardened steel so that they may better resist the friction imposed upon them by the blank as it is being forced into the die.

The batter plates 4'7 and 48 project over the working surface 46 of the forming block 46, to form a flange, the outer surface 50 of which is formed as an arc whose center coincides with the center of the arc 46' of the forming block 46.

block 46 by the bolt 44 which also holds the assembly on the bed plate 30.

The movable die member is similarly constructed and comprises a forming block 61 which has an arcuate forming surface 62 and which is provided with batter plates 63 and 64 which, like the batter plates 4'? and 48, are preferably made of hardened steel so that they will better resist wear. The plates 63 and, 64 project from the arcuate working surface 62 of the forming block 61 and terminate in an arcuate edge 65 which is formed on a radius the center of which coincides with the center of theforming block 62. Bolts 68 hold these members 61, 63 and 64 together, and since the assembly must be movable with respect to bed plate 30, the bolts are threaded into the plate 64 and do not touch the plate 30 Clamping members 66 and '67 are disposed on opposite sides ofthe movable forming die 60, those members cooperating with the members 43 and 42, respectively, to grip the cylindrical end sections of the blank to hold them in alignment during the operation of the machine.

As will best be seen in Figure 12, the clamping member 42 terminates in two flange-like projections 52 and 55 and the clamping member 6'? terminates in a tongue-like member 54 which fits inside of the members 52 and 55. The web section of the flange of the member 42 is formed arcuately to conform to the exterior surface of the blank and the end of the tongue section 54 of the member 67 is similarly formed to this same section.

When the movable clamping member 67 is extended to its completely operated position, in

which it is shown in Figure 12, the surfaces 56 adjacent the projecting tongue 54 strike against the extreme end of the flanges 52 and 55, serving to limit the movement of the member 67. At this time, the extreme ends of the projecting tongue 54 fall a little short of meeting the web section of the member 42, so that the blank is not tightly gripped by the clamping members.

The movable die 60 is carried on the end of the ram 6, and as will be seen in Figures 5, 6, 8 and 10, the connection between the ram and the die member is adjustable. The end of the ram is threaded as shown at '70, and a threaded coupling member 71 is screwed into the threaded opening in the ram and locked therein by a lock nut '72. The end of this coupling member '71 adjacent the die member 60 is provided with an annular groove 73 interposed between the main portion 74 of the member and the head portion '75. Two plates 76 and 77 are provided each with a semi-circular indentation the radius of which corresponds to the radius of the bottom section of the groove 73, these plates being attached to the end of the die 60 by a screw or bolt '78 which rigidly holds these plates on the die and establish a connection between the coupling member '71 and the die structure 60. A batter plate '79 made of hardened steel is interposed between the plates '76 and 7'7 and the end of the block'61 and held in place by bolts 78. The head of the rod '74 bears against this plate.

By suitable adjustment of the coupling member 71, the ram 6 and the die 60 can be brought,

into proper relation with respect to each other to permit the surfaces 56 of the die to rest against the flanges 52 and 55 of the stationary die when the ram 6 is in its fully operated position.

The punches 80 which cooperate with the dies 40 and 60 to form the blank into the desired shape, consist of L-shaped supports 81 and 82 which are laid on the bed plate 30 with their longer legs against that plate. As will be seen in Figure 9, the bed plate 30 is provided with a longitudinal slot 83 which is of rectangular cross section and into which the long leg of the support 81 is fitted and guided. Similarly the long leg of the support 82 is fitted in this slot 83 and guided thereby.

The shorter and up-turned legs of the supports 81 and 82 are abutted against each other, and disposed with their outward faces substantially normal to the face of the bed plate 30. These supports 84 and 85 serve as a mounting means upon which the forming blocks 86 and 87 are mounted in any convenient manner such as by the screws 88. These forming blocks 86 and 87 when fitted together form an oval shaped punch of such dimension as will fit within the broad side walls of the blank after that blank has been preliminarily separated in the manner pointed out in my copending application, Case 17.

The upper surface of the punch 86 is cut awaywedge block being forced upward by the bevel surface 89 as the punch is made to enter the die to thereby increase the height of the punch to its maximum value which is sufllcient to properly form the blank into the desired shape.

When the punch is being withdrawn from the die, in the manner which will hereinafter be brought out, the wedge block 90 slides downward on the bevel surface 89 to contract the vertical height of the punch to thereby permit withdrawing the punch from the finished work. The heads of the screws 91 limit this downward movement of the block, and since those bolts are projected through clearance holes in the block 90, the wedge block is capable of an upward movement as well as an outward movement with respect to the block 86.

Similarly, the forming block 87 is provided with a tapered surface 92 upon which the wedge block 93 is positioned and held by the bolts 94, those bolts likewise being projected through clearance holes which permit lateral and vertical movement of the wedge block 93 with respect to the forming block 87.

The abutting surfaces of the vertically disposed legs 84 and 85 of the supports 81 and 82 are cut away to form a tapered slot 95 the edges of which are provided with dovetails 96. The wedge carried by the ram 12 is machined to fit within this beveled slot 95 and contains dovetails 101 which register with the dovetails 96 of the support members, in such a manner that the supports are separated by a downward movement of the wedge 100 and contracted through the action of the dovetails by an upward movement of that wedge.

Preferably, the wedge consists of a central block 102 on opposite sides of which the hardened plates 103 are placed and held by through bolts 104, so that the friction encountered in the operation of the wedge against the supports 81 and 82 is taken up by the hardened plates 103, which can be renewed or resurfaced as the occasion demands. The bed plate 30 is provided with an opening 105 and the frame 1 with an opening 106 registering therewith and into which the point of .the wedge 100 can project when it is in its lowermost position and the punches 80 are spread into the dies 40 and 60.

The block 45 against which the stationary guide 40 is abutted is located immediately above the upper surface of the foot of the support 82, to resist any tendency of that foot to rise up off of the bed plate 30 when the wedge is moving downward. The pressure flanges 4 on the frame work are separated to leave a groove 107 between them into which the end of the foot 82 can project, and a plate 108 is provided on the outward end of the flanges 4 and held thereon by the bolts 109 which project through the flanges and into the plate 45, to guard against the possibility of injury to the end of the foot 82 while it is projecting into the slot 107.

In the operation of the machine, the blank is placed over the punches 86 and 87, in the manner shown in Figure 5, and is brought to bear upon the upper surfaces of the positioning blocks 110 and 111, which blocks are fastened onto the supports 81 and 82, respectively, by screws 112. Preferably, the blocks 110 and 111 are hardened metal, such as steel, so that the wear of the block will be minimized and the blanks will therefore be properly located in the machine.

When the punches are expanded, into the position in which they are shown in Figure 6, the blocks 110 and 111 slide into grooves 113 and 114 in the batter plates 84 and 48, respectively, these grooves being sufllciently large to permit free entrance and departure of the plates from them without friction.

The operation of the machine is as follows:

The slotted tubular blank is first heated to forging temperature, preliminarily spread in the manner pointed out in my copending application, Case 17, and transferred from that machine to the machine shown in the drawings of the instant application. The blank is slipped over the forming punches 86 and 87, the parallel walls 120 and 121 of the blank cpming to rest upon the upper surface of the positioning blocks 110 and 111. It will be remembered that in the straightening of these walls 120 and 121 in the previous step of the process, the upper and lower edges of the walls were stretched at their mid-section, and as a consequence are somewhat thinner than the midsection of the walls.

The lever 17 is operated to cause pressure from a pressure source, not shown, to be admitted to the cylinder 5 to force the ram 6 to the right, Figures 5, 6 and 8, thereby moving the movable die 60 to the right. The projecting tongue 54 of the clamping member of this die engages the end section 122 of the blank, and the corresponding tongue on the clamping member 67 engages the end section 123 of the blank. Simultaneously, the arcuate faces of the forming flanges 63 and 64 of the movable die engage the upper and lower edges of the wall 120 of the blank. As the ram 6 continues to move forward, the punches 86 and 87 and their supporting members 81 and 82,

the blank, and the movable die 60 are moved to the right by the movement of the ram. When the forward edge of the tongue 54 engages the flanges 52 and 55 of the stationary die, the forming edges 50 and 53 of the flanges 47 and 48 of that die engage the upper and lower edges of the wall 121 of the blank while the forming edges 65 of the flanges or batter plates 63 and 64 of the movable die engage the opposite wall of the blank, and the arcuate clamping surfaces of the stationary clamping members 43 and 42 engage the end sections 122 and 123 of the blank whereby the end sections are firmly clamped between the parts 43 and 42 of the stationary die and the cooperating parts 66 and 67 of the movable die, thus serving to securely hold the ends of the blank in proper position and alignment during the forging operation, as pointed out above. The flanges 52 and 55, cooperating with the surfaces 56 of the movable die, effectively prevent the pressure on the blank ends from becoming excessive or the ends too tightly gripped. When these steps have been performed the machine has then completed the first step of its operation, and the ram 6 is brought to rest.

In the preferred embodiment of the invention, the pressure that has been operating the ram 6 is now automatically shunted into the cylinder 11 to operate the ram 12 to push it downward and thereby bring the wedge 100 into engagement with the wedge-shape notch 95 in the punches 86 and 87. As the ram 12 continues in its downward movement, the punches are separated, and the walls 120 and 121 of the blank are folded into the dies 60 and 40, respectively.

During the first part of the travel of the punches from the position in which they are shown in Figure 5 to the position in which they are shown in Figure 6, the upper and lower edges of the walls 120 and 121 me folded over onto the upper and lower surfaces respectively of the punch members, this folding gathering metal in the flange at the points 125 and 126,those being the points which were stretched during the preliminary spreading of the walls 121 and 122 in the machine disclosed in my copending application, Case 17.

As the punches 86 and 8'7 continue moving into the die, the web sections 127 and 128 of the walls 121 and 122, respectively, are stretched to'increase their length and to flt them into the inside surface of the dies as shown in Figuresfi and '7. The stretch of metal during this step of the process occurs at points 128, .129 and 130 which are at the junction of the cylindrical end sections 122 and 123 and the transverse central cylindrical section of the blank. The clamping members and die forming blocks engage the sides of the blank at this point, but leave the upper and lower surfaces of the blank free so that the movement of metal is confined to those surfaces engaged by the die members.

Referring to Figure 14, metal is gathered in the flange of the blank at points 125 and 126, and stretching occurs at the points V129 and 130, this stretching being confined to the opposite sides 131 and 132 of the region 129 and to the points 133 and 134 of the region 130.

Prior to the forming of the banjo'in the blank, the regions through the ends of the end sections 122 and 123 were frustro-conical in shape, and after the metal has been stretched and flattened at points 130-134, inclusive, these sections assume a somewhat oval shape from the upper and lower faces of which project the regions of undisturbed metal 135 and 136. The forming of this particular region is carried out in the so-called throating operation which is described in my copending application, Case 19.

By'proper design of the dies, and choice of wall thiclmess and size of the blank, the stretching of metal at the points 130-134 is reduced to a minimum so that the wall thickness and strength of the metal in the critical section of the blank is not greatly impaired.

After the ram 12 has moved to its lowermost position and the wedge 100 operated to fully expand the punches into the dies, pressure in the cylinder 11 is reversed so that the ram 12 is raised.

During the downward operation of the wedge 190, the wedge blocks and 93 on the punches were forced up over the inclined surfaces 89 and 92, respectively, to expand the vertical height of the forming dies 86 and 87 to its maximum, which maximum fits the punch in the dies with sufflcient clearance between the two to permit the flanged edge of the walls 120 and 121 of the blank to fit therebetween.

When the ram 12 starts in an upward direction, the dovetail connection between the members 101 of the wedge and 96 of the punches retracts the punches from the die, the first movement of retraction sliding the wedge blocks 90 and 93 downward on their inclined surfaces 89 and 92, respectively, causing them to shrink the outside dimension of the punch so that it may be withdrawn from the flanged walls of the blank without injury to those walls.

The wedge 100 continues to rise as the ram 12 is moved upward, clearing itself from the punches when those punches are completely closed. When the ram 12 has reached its uppermost position in which it is shown in Figures 2 and 5, the pressure in cylinder 5 is released and the ram 6 retracted into that cylinder to thereby withdraw the movable die member 60 from the stationary die member 40. The end sections 122 and 123 are free of the die, and may be pulled out to clear the blank from the stationary portions of the die, this'movement also sliding the punches on the bed plates '30 into the position in which they are shown in Figures 2 and 5. The blank may then be removed from the press, and another blank substituted therefor and the hereinbefore enumerated steps in the operation repeated on that blank.

The particular design of the machine shown herein is made with the view of speedy operation:

so that the forging operation herein disclosed and the forging operation disclosed in my copending application, Case 17, may both'be carried on with one heating of the blank, that is, the two forging operations are performed at such a speed that they are completed before the blank has had time to cool sufficiently to necessitate its being reheated for the second forging operation.

While I have chosen to show my invention in connection with a preferred embodiment of it, I am aware that there are many modifications that can be made by one skilled in the art, and am therefore not to be limited to the specific disclosure but rather only by the scope of the appended claims.

therefrom, which comprises, holding the armsagainst bending out of alignment while allowing them freedom for longitudinal movement, forming a channel section at the central portion by holding the top and bottom thereof while forcing the intermediate metal outward thus folding the top and bottom thereof inward, and then continuing the outward forcing of the web of the channel until the flanges are drawn radially out ward by an amount approximating the width of the flanges.

2. The method of forming a channel shaped banjo casingfrom a metal'blank comprising a central cylindrical portion having a pair of arms extending therefrom, which comprises, folding the edges of the central portion inward between a pair of mating dies and then drawing the web of the channel; and with it the flanges, outwardly by an amount approximating the width of the flanges.

3. The method offorming a channel shaped banjo casing from a metal blank comprising a central cylindrical portion having a pair of arms extending therefrom, which comprises, folding the edges of the central portion inward between a pair of mating dies and then drawing the web of the channel, and with it the flanges, outwardly by an amount approximating the width of the flanges while maintaining the flanges of the channel confined between the pair of dies.

4. The method of forming a channel shaped banjo casing from a metal blank comprising a central cylindrical portion having a pair of arms extending therefrom, which comprises, holding the arms against bending out of alignment while permitting longitudinal movement of the arms, folding the edges of the central portion of the blank between a pair of external and internal mating dies, then expanding the internal die to expand the web of the channel and with it the flanges by an amount approximating the width of a metal blank comprising a central cylindrical portion having a pair of arms extending therefrom, which comprises, holding the arms and the top and bottom of the central portion, folding the edges of the central portion to produce a channel section by expanding a die within the central cylindrical portion to stretch outwardly 

